Dark grey soda-lime-silica glass composition which is intended for the production of glazing

ABSTRACT

The invention relates to a dark gray soda-lime silicate glass composition which includes a coloring part essentially consisting of the compounds below in contents varying within the following weight limits: 
                                   Fe 2 O 3  (total iron)   0.7 to 0.95%         CoO   50 to 80 ppm         NiO   400 to 700 ppm                             
or
 
                                   Fe 2 O 3  (total iron)   0.7 to 0.95%         CoO   200 to 300 ppm         NiO   1500 to 1900 ppm                             
said composition being free of selenium, having a redox of 0.40 or less, and the glass having a light transmission factor (T LA ) under illuminant A of 50% or less and an overall energy transmission factor (T E ) of less than 45%, these being measured for a thickness of 3.85 mm.
 
     The invention also relates to glass sheets, optionally thermally toughened, obtained from the aforementioned composition and to glazing comprising at least one of these sheets, especially as “privacy” windows for automobiles.

The present application is the U.S. counterpart of WO 05/095297, thetext of which is incorporated by reference, which claims as priorityFrench Application No. 04/02898, filed on Mar. 9, 2004, the text ofwhich is incorporated by reference.

The invention relates to a soda-lime silicate glass composition of darkgray color, in particular for producing flat glass by the float processon a bath of molten metal, this glass being intended to form windows forthe automobile and building industries. Although more particularlydescribed with reference to automobile applications, the invention ishowever not limited to this field.

Windows intended for the automobile industry are subjected to variousrequirements, especially as regards their optical properties. Theserequirements are governed by regulations, for example as regards thelight transmission of a windshield, or they emanate from automobilemanufacturers, for example when the aim is to impose a particular color,for esthetic reasons, or energy transmission values for the sake ofimproving passenger comfort.

The glazing provided for the rear part (side and rear windows) or theroof of an automobile must in particular meet the followingrequirements: it must have an esthetically pleasing gray color, ensuringgood color rendition through the glazing, and possess protectiveproperties with respect to solar radiation, namely a low energytransmission, especially as regards infrared radiation, so as to avoidthe greenhouse effect inside the passenger compartment, and a moderatelight transmission (less than about 50%) so as to provide users with afeeling of intimacy. Usually, these windows also have a low ultravioletradiation transmission in order to prevent degradation of the interiorfurnishings. Such glass is also called “privacy” glass.

Automobile windows made of soda-lime silicate glass are in generalmanufactured under the “float” process conditions, in which the moltenglass floats on a bath of molten metal, usually tin, in order to form aribbon that is then cut into the form of glass sheets. These sheets maysubsequently by bent or undergo a treatment with a view to improving themechanical properties of the glass, for example a thermal tougheningoperation.

The level of coloration and the performance requirements indicated aboveare achieved by the addition of coloring agents into the batch materialsintended to be melted in order to produce the soda-lime silicate glassmatrix. Many combinations of a relatively large number of coloringagents have been proposed in order to produce gray “privacy” glass.

Glass compositions containing iron, cobalt, nickel and selenium aredescribed in EP-A-947 476, EP-A-1 020 414 and EP-A-1 125 899. The amountof selenium in the glass varies from 0.0008 to 0.0050%.

However, such glass is undesirable owing to the presence of selenium insubstantial amount, and the drawbacks that stem therefrom.

Firstly, it is known that selenium exists in the glass in several stableoxidation states, some of which give the glass a particular coloration(relatively intense pink, red or amber). In addition, the final colordepends on the nature of the other colorants present in the glass, withwhich selenium can be combined: for example, Se²⁻ forms a chromophorewith the ferric ions, which gives the glass a red-brown coloration. Tocontrol the tint therefore requires the redox to be very preciselycontrolled within a relatively narrow range of values.

Next, the temperature within the furnace in which the glass batch ismelted is very much greater than the selenium vaporization temperature.It follows that most of the selenium (about 90%) is in the atmosphere ofthe furnace, which means that the stacks have to be equipped withelectrostatic filters for retaining the selenium present in the fluegases and the dust. Added to the already very high cost of thesefiltration devices is the problem of recycling the dust retained by thefilters, only some of which can be reintroduced into the furnace.

Finally, selenium has a high toxicity, even at low concentration, whichmeans that special measures are required in order to be able to handleit.

Other glass compositions have been proposed which combine iron, cobalt,nickel and titanium, as a replacement for all or part of the selenium(see EP-A-842 206, EP-A-849 233 and JP-A-200247679). The amount oftitanium in the form of TiO₂ to be introduced into the glass remainshigh, from 0.7 to 2.3%.

Such glass is not advantageous from the economic standpoint as titaniumis an expensive compound, which is a major contribution to the costprice of the composition. Furthermore, titanium gives windows an oftenundesirable yellow coloration.

Glass compositions of a low selenium content, which combine iron, cobaltand nickel, have also been described.

In EP-A-825 156 and US-A-2003/50175, the glass compositions proposedhave a high iron content, varying from 1.2 to 2.2% and from 0.95 to1.2%, respectively. The high iron content, particularly in the form ofFeO, results in a reduction in heat transfers in the glass bath,resulting in lower heating efficiency of the glass in the furnace. Thissubstantial reduction in temperature is palliated in furnaces withoverhead burners by placing, for example, electrodes on the furnacefloor.

In WO-A-01/58820, the low iron content (0.25 to 0.65%) allows glasscompositions with a very neutral coloration to be obtained, but theseare not very selective.

Finally, EP-A-653 388 describes glass compositions containing iron,cobalt and nickel, and optionally selenium. The iron content varies from0.15 to 1.2%. According to the examples, the low selenium contents areassociated with iron contents that are not overly high, less than 0.5%,giving the glass a high energy transmission.

One object of the present invention is to propose a dark gray soda-limesilicate glass composition containing no selenium, which can be used toform windows, in particular “privacy” windows for automobiles, thiscomposition having optical properties similar to those of knowncompositions that contain selenium and/or titanium.

Another object of the invention is to obtain a glass composition free ofselenium and titanium that can be produced under the conditions of thefloat process.

According to the present invention, these objects are achieved by theglass composition which includes a coloring part essentially consistingof the compounds below in contents varying within the following weightlimits:

Fe₂O₃ (total iron) 0.7 to 0.95% CoO 50 to 80 ppm NiO 400 to 700 ppmFe₂O₃ (total iron) 0.7 to 0.95% CoO 200 to 300 ppm NiO 1500 to 1900 ppmsaid composition being free of selenium, having a redox of 0.40 or less,and the glass having a light transmission factor (T_(LA)) underilluminant A of 50% or less and an overall energy transmission factor(T_(E)) of less than 45%, these being measured for a thickness of 3.85mm.

As indicated above, the glass falling within the scope of the presentinvention is gray glass, that is to say it has a transmission curve as afunction of the visible wavelength that is practically invariant.

In the CIE (International Lighting Commission) system, gray substancesdo not have a dominant wavelength and their excitation purity is zero.By extension, any substance whose curve is relatively flat in thevisible range, but which nevertheless has weak absorption bands allowinga dominant wavelength to be defined, and a low but nonzero purity, isgenerally accepted as being gray.

The gray glass according to the invention is consequently defined by itschromatic coordinates L*, a* and b* measured under the standardilluminant D₆₅ defined by the CIE, which represents average daylighthaving a color temperature of 6500 K, allowing the optical properties ofautomobile windows with a thickness of 3.85 mm to be evaluated. Theglass according to the invention is defined as follows:

-   -   L* varies from 30 to 80;    -   a* varies from −15 to 0; and    -   b* varies from −20 to +25.

The use of the aforementioned coloring agents within the limits of theinvention gives the desired dark gray coloration and also allows theoptical and energy properties of the glass to be optimally adjusted.

The action of the colorants taken individually is in general welldescribed in the literature.

The presence of iron in a glass composition may result from the rawmaterials, as impurities, or from an intentional addition with the aimof coloring the glass. It is known that iron exists in the form offerric (Fe³⁺) ions and ferrous (Fe²⁺) ions. The presence of Fe³⁺ ionsgives the glass a slight yellow coloration and allows ultravioletradiation to be absorbed. The presence of Fe²⁺ ions gives the glass amore pronounced green-blue coloration and induces absorption of infraredradiation. The increase in iron content in both its forms increases theabsorption of radiation at the extremities of the visible spectrum, thiseffect taking place to the detriment of light transmission. Conversely,by reducing the proportion of iron, particularly in Fe²⁺ form, theperformance in terms of energy transmission is degraded, while the lighttransmission increases.

In the present invention, the total iron content in the composition isbetween 0.70 and 0.95%, preferably between 0.80 and 0.95%. An ironcontent of less than 0.70% does not allow the intended performance to beachieved, especially because the T_(LA) and T_(E) values are too high(or the infrared selectivity is too low). Above 0.95% iron, theconditions for melting the glass composition become difficult owing tothe high FeO content, which limits heat transfer.

The relatively moderate iron content used in the compositions accordingto the invention makes it possible, while still imparting a low energytransmission, to have an a* value that is not too high, and often closeto zero, which gives the glass not too green a shade. In particular,when the glass is intended to be thermally toughened, it is beneficialto have an a* value of greater than −12, as this tends to approach 0after toughening, which means that the glass becomes more neutral.

Cobalt produces an intense blue coloration and also decreases the lighttransmission. Its amount in the glass must therefore be perfectlycontrolled in order to make the light transmission compatible with theuse for which the glass is intended. According to the invention, thecobalt oxide content varies from 50 to 80 ppm, or from 200 to 300 ppm.

Nickel oxide gives the glass a brown coloration. In the presentinvention, the nickel oxide content is limited so as to prevent it frombeing able to be combined with sulfur compounds coming from the rawmaterials or from other compounds intentionally added (especiallysulfate as refining agent), forming nickel sulfide balls. It is in factknown that the “high temperature” phase of nickel sulfide, which is“frozen in” during thermal toughening, may progressively be transformedinto a “low temperature” phase, the larger size of which inducesmechanical stresses that shatter the glass, hence the risk of anaccident. Thus, the nickel oxide content does not exceed 1900 ppm forreasons associated in particular with the toughening operation, asindicated in the rest of the text. According to the invention, thenickel oxide content varies from 400 to 700 ppm or from 1500 to 1900ppm, depending on the cobalt oxide content. As a general rule, it isdifficult to predict the optical and energy properties of a glass whenit contains several coloring agents. These properties result in factfrom a complex interaction between the various agents, the behavior ofwhich is directly linked to their oxidation state and to the subsequenttreatments (toughening, annealing, etc.) that the glass may have toundergo.

In the present invention, the choice of colorants, their content andtheir oxidation/reduction state is key in obtaining the intended darkgray coloration and the optical properties.

The redox defined by the ratio of the weight content of ferrous oxide(expressed as FeO) to the weight content of total iron (expressed asFe₂O₃) is generally maintained at 0.40 or less, preferably of 0.30 orless, for reasons essentially associated with the melting and refiningof the glass.

The redox is generally controlled using oxidizing agents such as sodiumsulfate and reducing agents such as coke or calumite, the relativecontents of which are adjusted in order to obtain the desired redox.

The composition according to the invention may furthermore contain lessthan 1%, preferably less than 0.5%, of coloring agents other than iron,cobalt and nickel, chosen from copper oxide, chromium oxide, titaniumoxide, vanadium oxide and mixtures thereof.

Titanium oxide gives the glass a yellow tint and results in a reductionin the ultraviolet radiation transmission, by interacting with ferrousoxide. Consequently, its content is preferably maintained at a valuebelow 0.5%, preferably below 0.3%. Advantageously, the glass accordingto the invention does not contain titanium oxide other than thatintroduced by way of impurity by the batch materials, corresponding to acontent of less than 0.2%, or less than 0.1%, and even less than 0.05%.

Preferably, the glass composition according to the invention includes nocoloring agent other than iron, cobalt and nickel.

The composition according to the invention makes it possible to obtain aglass possessing an overall light transmission factor T_(LA) of 50% orless, preferably less than 40%, by and better still greater than 5%.

According to the invention, the glass has an overall energy transmissionfactor T_(E) of less than 45%, preferably less than 30%.

A first series of preferred glass compositions according to theinvention includes a coloring part essentially consisting of thecompounds below, in the following weight limits:

Fe₂O₃ (total iron) 0.80 to 0.95% CoO 50 to 80 ppm NiO 400 to 700 ppmRedox 0.20 to 0.30.

These compositions make it possible to obtain glass having a T_(LA)value of around 30 to 45%. Such glass gives the occupants of motorvehicles equipped with it a feeling of intimacy and security.

Another series of preferred glass compositions according to theinvention includes a coloring part essentially consisting of thecompounds below, in the following weight limits:

Fe₂O₃ (total iron) 0.80 to 0.95% CoO 200 to 300 ppm NiO 1500 to 1900 ppmRedox 0.20 to 0.30.

These compositions make it possible to obtain glass having a lowerT_(LA) value, of around 6 to 12%. Such highly tinted glass can be usedfor example as automobile roofs.

The term “soda-lime silicate” is used here in a broad sense and relatesto any glass composition consisting of a glass matrix that comprises thefollowing constituents (in percentages by weight):

-   -   SiO₂ 64-75%    -   Al₂O₃ 0-5%    -   B₂O₃ 0-5%    -   CaO 5-15%    -   MgO 0-10%    -   Na₂O 10-18%    -   K₂O 0-5%    -   BaO 0-5%.

It is recommended here that the soda-lime silicate glass composition mayinclude, apart from the inevitable impurities contained especially inthe batch materials, a small proportion (up to 1%) of otherconstituents, for example agents (SO₃, Cl, Sb₂O₃, AS₂O₃) that help inmelting or refining the glass or that come from the optional addition ofrecycled cullet into the glass batch.

In the glass according to the invention, the silica content is generallymaintained within narrow limits for the following reasons. Above 75%,the viscosity of glass and its ability to devitrify greatly increase,which makes it more difficult for the glass to melt and to flow on thebath of molten tin. Below 64%, the hydrolytic resistance of the glassrapidly decreases, and the transmission in the visible also decreases.

The alkali metal oxides Na₂O and K₂O facilitate melting of the glass andallow its viscosity at high temperatures to be adjusted so as to keep itclose to that of a standard glass. K₂O can be used up to 5%, as abovethis the problem of the high cost of the composition arises. Moreover,the K₂O content may only be increased, for the most part, to thedetriment of the Na₂O content, which helps to increase the viscosity.

The sum of the Na₂O and K₂O contents, expressed as percentages byweight, is preferably equal to or greater than 10% and advantageouslyless than 20%. If the sum of these contents is greater than 20% or ifthe Na₂O content is greater than 18%, the hydrolytic resistance isgreatly reduced.

Alkaline-earth metal oxides allow the viscosity of the glass to bematched to the production conditions.

MgO may be used up to about 10% and its omission may be at least partlycompensated for by an increase in the Na₂O content and/or the SiO₂content. Preferably, the MgO content is less than 5% and particularlyadvantageously is less than 2%, which has the effect of increasing theinfrared absorption capacity without impairing the transmission in thevisible.

BaO allows the light transmission to be increased and it can be added tothe composition with a content of less than 5%.

BaO has a much smaller effect than CaO and MgO on the viscosity of theglass and an increase in its content is essentially to the detriment ofthe alkaline-earth oxides, MgO and most particularly CaO. Any increasein BaO helps to increase the viscosity of the glass at low temperatures.Preferably, the glass according to the invention contains no BaO.

Apart from complying with the limits defined above for the variation inthe content of each alkaline-earth metal oxide, it is preferable inorder to obtain the desired transmission properties to limit the sum ofthe MgO, CaO and BaO percentage weight contents to a value of 15% orless.

The composition according to the invention may furthermore includeadditives, for example agents that modify the optical properties withincertain parts of the spectrum, especially within the ultraviolet range,such as CeO₂, WO₃ and La₂O₃. The total content of these additives doesnot in general exceed 2% by weight of the composition, and preferablydoes not exceed 1%.

The glass composition according to the invention can be melted underfloat glass or rolled glass production conditions. The melting generallytakes place in fired furnaces, optionally provided with electrodes forheating the glass through the bulk by passing an electric currentbetween the two electrodes. To facilitate melting, and especially tomake this mechanically beneficial, the glass composition advantageouslyhas a temperature corresponding to a viscosity η such that log η=2 whichis less than 1500° C. More preferably, the temperature corresponding tothe viscosity η such that log η=3.5 (denoted by T(log η=3.5)) and theliquidus temperature (denoted by T_(liq)) satisfy the equation:T(log η=3.5)−T _(liq)>20° C.and better still:T(log η=3.5)−T _(liq)>50° C.

The thickness of the glass sheet formed generally varies between 1 and19 mm.

In the float process, the thickness of the ribbon obtained by sheetingout the molten glass on the tin bath preferably varies between 1 and 5mm for automobile windows and between 3 and 10 mm for glazing intendedfor buildings.

By rolling, the thickness of the glass preferentially varies between 4and 10 mm.

The glass sheet obtained by cutting the glass ribbon may subsequentlyundergo a bending and/or toughening operation.

Thermal toughening is a well-known operation that consists in heatingthe glass sheet to a temperature of around 600 to 700° C. for a timethat does not generally exceed a few minutes and in suddenly cooling it,for example by pressurized air jets.

The toughened glass sheet obtained from the composition according to theinvention is noteworthy in that it has a dark gray colorationcharacterized in particular by an a* value varying from −10 to 0 and ab* value varying from −20 to +15, preferably from −5 to +5.

It is possible to vary the dark gray coloration of the toughened glassin order to give it a tint ranging from blue to bronze by adjusting therelative amounts of the coloring agents.

If the ratio R is defined as follows:R=[300Fe₂O₃+NiO]/[1200FeO+5CoO]in which the Fe₂O₃ and FeO contents are expressed as percentages byweight and the NiO and CoO contents are expressed in ppm (Fe₂O₃representing in this formula the ferric iron content), it is possible toobtain a glass having a bronze tint when the ratio R is greater thanabout 2.2 and a bluish tint when the ratio is less than 0.6. When thevalue of R lies between these limits, preferably between 0.8 and 1.5,the glass possesses a particularly advantageous neutral tint.

Under the thermal toughening conditions, the variation in the color ofthe glass is adjusted by the relative NiO content. It has been foundthat, in the toughened glass, the chemical environment of the nickel ismodified, giving it different absorption properties. This results in anincrease in the a* value and a decrease in that of b* and consequently ashift in the coloration of the glass toward more neutral tints. Thesechanges are greater the higher the NiO content.

The glass sheet obtained may also undergo other subsequent treatmentoperations, for example for the purpose of coating it with one or moremetal oxide films for the purpose of reducing its heat-up by solarradiation.

The optionally toughened glass sheet can be used as such or can becombined with another glass sheet to form laminated glazing forautomobiles or buildings.

The examples of the glass compositions given below give a betterappreciation of the advantages of the present invention.

In these examples, the values of the following properties calculatedfrom experimental spectra for a glass thickness of 3.85 mm areindicated:

-   -   the overall light transmission factor (T_(LA)) under illuminant        A, together with the chromatic coordinates L*, a* and b* under        illuminant D₆₅, integrated between 380 and 780 nm. These        calculations are carried out taking the CIE 1931 calorimetric        reference observer;    -   the overall energy transmission factor (T_(E)) integrated        between 295 and 2500 nm according to the ISO 9050 standard        (PARRY MOON, air mass 2);    -   the redox, defined as being the ratio of the mass content of        ferrous iron (expressed as FeO) to the mass content of total        iron (expressed as Fe₂O₃). The total iron content is measured by        X-ray fluorescence and the ferrous iron content is measured        using wet chemistry.

Each of the compositions given in Table 1 was produced from thefollowing glass matrix, the contents of which are expressed inpercentages by weight, this being corrected as regards silica in orderto be matched to the total content of coloring agents added:

-   -   SiO₂71%    -   Al₂O₃ 0.70%    -   CaO 8.90%    -   MgO 3.80%    -   Na₂O 14.10%    -   K₂O 0.10%.

The glass obtained was thermally toughened by heating in a furnace at600-700° C. for 1 to 3 minutes, and was then cooled by nozzles blastingair at a pressure of 1 bar (0.1 MPa) for 1 minute.

All the glass compositions according to the invention (examples 1 to 13)were characterized by an overall light transmission factor (T_(LA)) ofbetween 5 and 50% and a dark gray coloration, these characteristicsbeing comparable to those obtained with a glass containing seleniumand/or titanium.

In particular, the glass compositions of Examples 1 and 2 are verysimilar in terms of light transmission and color to the known glasscompositions of Examples A and B (comparative examples), respectively,used for automobile windows, although the latter have appreciableselenium contents of 10 and 30 ppm, respectively.

Examples 1, 7 and 9 to 13 illustrate a first embodiment of theinvention, in which the CoO and NiO contents vary from 50 to 80 ppm andfrom 400 to 700 ppm, respectively. Such glass has, after thermaltoughening, light transmission factors of around 30 to 45%, which allowsthem to be used as side or rear windows for automobiles, or as windowsfor buildings.

Examples 2 to 6 illustrate a second preferred embodiment of theinvention, for which the CoO and NiO contents vary from 200 to 300 ppmand from 1500 to 1900 ppm, respectively, thus making it possible toobtain, after thermal toughening, glass having light transmissionfactors of around 6 to 12%. Owing to these low transmission values, suchglass is more particularly intended for the production of automobileroofs.

TABLE 1 Example A B 1 2 3 4 5 6 7 8 9 10 11 12 13 Fe₂O₃ 1.30 1.80 0.900.94 0.85 0.90 0.81 0.83 0.94 0.89 0.94 0.82 0.80 0.70 0.75 (%) Redox0.23 0.24 0.27 0.26 0.21 0.28 0.22 0.28 0.30 0.33 0.25 0.24 0.28 0.170.20 CoO 90 300 70 230 290 300 280 250 76 60 52 65 50 70 60 (ppm) NiO 00 590 1590 1900 1780 1790 1650 690 530 690 610 550 520 520 (ppm) R⁽⁺⁾1.21 1.24 1.26 1.09 1.20 1.19 1.22 1.07 1.64 1.40 1.39 1.40 1.45 Cr₂O₃ 0100 (ppm) Se 10 30 (ppm) After tough- ening T_(LA) (%) 35.0 10.0 35.810.2 6.8 6.7 7.5 8.9 31.1 36.8 35.1 37.2 40.4 42.2 42.5 T_(E) 22.0 8.227.4 15.1 16.3 12.6 15.6 14.7 22.7 24.9 26.5 30.6 30.6 41.3 37.7 L* 66.338.0 66.9 38.4 31.6 31.7 33.3 36.3 63.2 68.0 66.2 67.9 70.2 71.3 71.5 a*−7.5 −4.3 −7.3 −4.0 −2.2 −3.2 −2.6 −3.6 −8.3 −9.0 −7.4 −6.5 −7.1 −4.6−5.5 b* 2.9 1.3 3.0 1.3 −1.6 −4.2 −2.5 −2.0 2.4 0.9 6.6 3.6 3.7 2.5 3.4Before tough- ening T_(LA) (%) 38.7 12.3 8.9 8.7 9.7 11.3 34.4 39.7 38.840.6 43.7 45.5 45.8 T_(E) 28.0 15.4 17.1 13.3 16.5 15.6 23.9 25.9 27.631.7 31.7 42.4 38.8 L* 69.1 42.2 36.1 35.9 37.7 40.6 65.9 70.1 68.9 70.372.5 73.5 73.7 a* −9.8 −8.4 −6.6 −7.9 −7.1 −8.0 −10.7 −10.9 −9.5 −8.6−9.0 −6.4 −7.2 b* 5.6 6.2 5.7 2.6 4.6 4.8 6.3 4.0 10.6 7.2 7.1 5.8 6.7R⁽⁺⁾ = [300Fe₂O₃ + NiO]/[1200FeO + 5CoO]

1. A selenium-free gray soda-lime silicate glass having a redox of 0.40or less, a light transmission factor (T_(LA)) under illuminant A of 50%or less, and an overall energy transmission factor (T_(E)) of less than45%, wherein the T_(LA) and T_(E) are measured at a glass thickness of3.85 mm, comprising: a coloring component comprising: Fe₂O₃ (total iron)0.7 to 0.95%, CoO 50 to 80 ppm, and NiO 400 to 700 ppm.


2. The glass of claim 1, wherein the redox does not exceed 0.30.
 3. Theglass of claim 1, wherein the light transmission factor under illuminantA, T_(LA), is greater than 5%.
 4. The glass of claim 1, wherein theoverall energy transmission factor T_(E) is less than 30%.
 5. The glassof claim 1, further comprising 1% or less of coloring agents selectedfrom the group consisting of copper oxide, chromium oxide, titaniumoxide, vanadium oxide and mixtures thereof.
 6. The glass of claim 5,wherein the titanium oxide content is less than 0.5.
 7. The glass ofclaim 1, which comprises coloring agents: Fe₂O₃ (total iron) 0.80 to0.95% CoO 50 to 80 ppm, and NiO 400 to 700 ppm;

which has a redox of 0.20 to 0.30 and a light transmission factor underilluminant A (T_(LA)) of around 30 to 45%.
 8. The glass of claim 1,comprising the following constituents (in percentages by weight): SiO₂64-75% Al₂O₃ 0-5% B₂O₃ 0-5% CaO 5-15% MgO 0-10% Na₂O 10-18% K₂O 0-5%,and BaO 0-5%.
 9. A glass sheet comprising the glass of claim 1 which isformed by the float process on a bath of molten metal.
 10. The glasssheet of claim 9, which has the following chromatic coordinates measuredunder illuminant D₆₅, for a thickness of 3.85 mm: L* varies from 30 to80 a* varies from −15 to 0 b* varies from −20 to
 25. 11. A thermallytoughened glass sheet comprising the glass of claim 1 having thefollowing chromatic coordinates measured under illuminant D₆₅, for athickness of 3.85 mm: a* varies from −10 to 0 b* varies from −20 to +15,preferably from −5 to +5.
 12. The glass sheet of claim 9, furthercomprising at least one layer of at least one metal oxide for reflectinginfrared radiation.
 13. A window comprising at least one glass sheet ofclaim
 9. 14. The selenium-free gray soda-lime silicate glass of claim 1,wherein said coloring component consists essentially of: Fe₂O₃ (totaliron) 0.7 to 0.95%, CoO 50 to 80 ppm, and NiO 400 to 700 ppm.